Description: This shows the Photoelectric effect on a charged plate using a UV light and charge indicating needle.
- Phtotoelectric apparatus (electroscope and metal plate)
- UV light source
- Rod and fur
- Sand paper
- Optional: Flood light
- Sand one side of the metal plate.
- Place the metal plate into the top of the electroscope.
- Take the filter off the UV lamp.
- Charge the rod by rubbing it with the fur.
- Slide the rod against the plate; this should charge the plate and cause the needle to move
- Wait for the needle to calm down.
- Shine the flashlight on the plate (shiny side); the needle should not move.
- Optional: Shine the flood light onto the plate; the needle should still not move.
- Turn on the UV light and shine it on the metal plate (the shiny side); the needle should move.
- Turn off the UV light and put charge on the electroscope.
- Now, place the piece of glass in between the plate and the UV light source; nothing should happen.
- When finished, turn off the UV light.
- There are two different electroscopes that you can use for this demonstration. One is quite large, but requires more charge to deflect the needle.
- The electroscope should hold its charge during your lecture. However, when using the larger one, it is recommended to have another person charge the electroscope right before you demonstrate it.